Question: Solve for $x$ and $y$ using substitution. ${-2x-y = 7}$ ${x = -3y-11}$
Solution: Since $x$ has already been solved for, substitute $-3y-11$ for $x$ in the first equation. ${-2}{(-3y-11)}{- y = 7}$ Simplify and solve for $y$ $6y+22 - y = 7$ $5y+22 = 7$ $5y+22{-22} = 7{-22}$ $5y = -15$ $\dfrac{5y}{{5}} = \dfrac{-15}{{5}}$ ${y = -3}$ Now that you know ${y = -3}$ , plug it back into $\thinspace {x = -3y-11}\thinspace$ to find $x$ ${x = -3}{(-3)}{ - 11}$ $x = 9 - 11$ ${x = -2}$ You can also plug ${y = -3}$ into $\thinspace {-2x-y = 7}\thinspace$ and get the same answer for $x$ : ${-2x - }{(-3)}{= 7}$ ${x = -2}$